1. Technical Field of the Invention
The present invention relates generally to a sequentially joined-segment coil of a rotary electric machine and a production method thereof which ensures a high degree of electrical insulation.
2. Background Art
Sequentially joined-segment stator coils have been proposed which are made by conductor segments inserted in slots in a stator core whose ends are joined in sequence. For instance, Japanese Patent No. 3118837, assigned to the same assignee as that of this application, discloses a production method of joining U-shaped conductor segments in sequence to make a stator coil.
The sequentially joined segment stator coil, as taught in the above patents, is made by inserting a pair of legs of each conductor segment into two of slots of a core located at an interval away from each other which is substantially equivalent to a magnetic pole pitch of a rotor, bending end portions of the legs projecting from the slots in a circumferential direction of the core, and joining the end portions of the conductor segments in series.
The conductor segments each consist of a U or V-shaped head (also called a turn), a pair of side conductor portions extending from the head to be inserted into two of the slots of the core from an axial direction of the core, and end portions which project from the side conductor portions toward the other side of the slots and extend in the circumferential direction of the core. The projecting end portions are joined in pair. In the following discussion, the side conductor portion and the projecting end portion will also be referred to as a leg as a whole, the heads of the conductor segments will also be referred to as a segment head-side coil end of the stator coil, and the projecting end portions will also be referred to as a segment end-side coil end of the stator coil.
Japanese Patent Publication No. 3118837 also discloses a method of forming slant portions of a head of each of a small-sized conductor segment and a large-sized segment. The formation of the slant portions is achieved by fitting a total of four legs of a set of the small-sized conductor segment and the large-sized segment extending over the small-sized segment within two rings arrayed coaxially with each other and rotating the rings in opposite directions to spread the legs in circumferential directions of the rings.
Japanese Patent First Publication No. 2000-139049 discloses a method of forming the slant portions of the head of each conductor segment which is achieved by fitting a total of four legs of a set of the small-sized conductor segment and the large-sized segment extending over the small-sized segment within four rings arrayed coaxially with each other and rotating the rings in opposite directions to spread the legs of each conductor segment in circumferential directions of the rings.
Further, Japanese Patent First Publication No. 2001-45722 discloses a production method of the above small-sized conductor segment and the large-sized conductor segment.
The production methods of the sequentially joined-segment stator coil as taught in the above publications will be discussed below in detail.
First, a required number of pine needle-like conductor segments are prepared. Each of the conductor segments is formed into a U-shape one with side conductor portions extending at substantially a magnetic pole pitch interval away from each other. The side conductor portions of each conductor segment are placed spatially in alignment with two of the slots formed in the core, respectively, (i.e., in a circumferential direction of the core) for simultaneous insertion of the side conductor portions into the slots. These steps may be achieved with a pair of coaxially arrayed rings with slots, as illustrated in FIG. 3 of Japanese Patent No. 3118837. Specifically, legs of each conductor segment are fitted in two of the slots aligned in a radius direction of the rings. Next, the rings are turned relative to each other through a given angle equivalent to a magnetic pole pitch to spread the legs, thereby forming the U-shaped conductor segment.
Subsequently, the head of each of the U-shaped conductor segments is held. The legs are drawn from the slots and then inserted into the slots of the core.
Next, end portions of the legs projecting from the slots are bent in the circumferential direction of the core through half a magnetic pole pitch. Such bending may be achieved with a plurality of coaxially arrayed rings with slots, as illustrated in FIGS. 4 and 5 of Japanese Patent No. 03196738. Specifically, tips of the projecting end portions of the legs are inserted into the slots of the rings. The rings are rotated in the circumferential direction by half a magnetic pole pitch (i.e., an electrical angle of π/2) to bent the projecting end portions in the circumferential direction through half the magnetic pole pitch. It is advisable that the rotation of the rings be performed while urging the rings toward the projecting end portions (i.e., the axial direction of the core) for increasing the radius of curvature of the turn of each conductor segment. Next, the projecting end portions are welded in a given sequence, thereby forming an endless phase coil. Any one of the heads of the U-shaped conductor segments is cut to define coil terminals. If the coil terminals are made longer and bent in the circumferential direction, they may be employed as a neutral point connecting line. The reason that the coil terminals are provided in the segment head-side coil end is because if the coil terminals are provided in the segment end-side coil end, they will interface with welding of the end portions of the conductor segments.
The above sequentially joined-segment stator coil is usually employed as a stator coil of automotive ac generators and has suffered from the following drawback.
The spreading of the legs of the small-sized and large-sized conductor segments is, as described above, achieved by fitting the two legs of each conductor segment within a large one and a small one of the rings, respectively, and rotating the rings equi-angles in opposite directions. The head of each conductor segment before the legs are spread is caught by a pair of tines arrayed in the circumferential direction of the rings.
Each of the tines has a chamfered surface which is to abut the head of each conductor segment in order to avoid the damage to an insulating film or coating on the tip of the head of each conductor segment resulting from bending thereof in the circumferential direction of the rings by the tines during the rotation of the rings. However, when the outer and inner rings are rotated at the same angular speed or through the same angle, a difference in diameter of the outer and inner rings will cause an outer one of the legs placed in the outer ring to undergo tension stress stronger than that acting on the inner leg. The tension stress acts between the tip of the head of each conductor segment and a side portion of the chamfered surface of the tine abutting the tip, which causes the damage to the insulating coating on the tip.